Three regulatory genes control the expression of the structural genes for a family of enzymes concerned with phosphorus metabolism in Neurospora. We are continuing to study the mechanism of regulation by several approaches: (1) By use of dosage studies, we hope to learn more about how the regulatory genes interact with one another. Such studies seem to have shown already that the products of some regulatory genes react with one another, rather than the product of one regulatory gene interacting with a chromosomal site controlling the transcription of another regulatory gene. Much more needs to be done to show that this is the correct interpretation. (2) We are trying to detect the product of the nuc-1 gene (the ultimate regulatory gene for the phosphorus system) using two dimensional gel electrophoresis and double-label autoradiography. (3) We are trying to develop an in vivo or in cellulo assay for the functional nuc-1 product. (4) We are trying to get genetic evidence of the nature of another one of the regulatory macromolecules, the preg product. BIBLIOGRAPHIC REFERENCES: Lehman, John F. and Metzenberg, Robert L., Regulation of phosphate metabolism in Neurospora crassa: identification of the structural gene for repressible alkaline phosphatase. Genetics, in press. Nelson, Robert E., Lehman, John F., and Metzenberg, Robert L., Regulation of phosphate metabolism in Neurospora crassa: identification of the structural gene for repressible acid phosphatase. Genetics, in press.